1. Field of the Invention
The present invention relates to a drive motor capable of outputting both rotary motion and linear motion, as well as to a drive apparatus for a molding machine utilizing the drive motor.
2. Description of the Related Art
Conventionally, a so-called pre-plasticization-type injection molding machine is known (see Japanese Patent Application Laid-Open (kokai) No. 8(1996)-25437. Such an injection molding machine includes a plasticizing unit for plasticizing and melting a molding material as well as an injection unit for injecting and charging melted resin into a mold.
In such a pre-plasticization-type injection molding machine, a molding material is supplied from a hopper to the interior of a barrel of the plasticizing unit, and the molding material is plasticized and melted by rotation of a screw disposed within the barrel. The thus-melted resin is discharged from a resin exit provided at the tip end of the barrel to be fed, via a resin passage portion, to the interior of the tip end portion of an injection cylinder of the injection unit. The thus-fed resin is measured and accumulated within the injection cylinder. During measuring, an injection plunger of the injection cylinder retracts. After completion of measuring, the injection plunger is advanced in order to inject and charge the resin into a cavity of a mold.
The pre-plasticization-type injection molding machine involves a problem in that during injection, the measured resin flows backward via the resin passage portion to the interior of the barrel. Therefore, a valve section is added to the resin passage portion in order to open and close the resin passage. During measuring, the valve section is opened in order to allow passage of resin, and during injection, the valve section is closed in order to shut off the resin passage, thereby preventing backflow of the resin at the resin passage portion.
In such a conventional pre-plasticization-type injection molding machine, a valve section is added to the resin passage portion, and a drive section for opening and closing the valve section is provided. Therefore, the resin passage portion must be formed to have a special internal structure and shape. Further, a dedicated drive section for opening and closing the valve section, such as a hydraulic cylinder, must be provided. This results in a complex structure of the resin passage portion, decreased reliability, and increased cost.
When a movable portion is driven to effect both rotary motion and linear motion in a motor-driven molding machine, each motion generally requires one drive motor. Further, a drive system for advancing and retracting a movable portion requires, in addition to a drive motor, a motion conversion mechanism such as a ball screw mechanism for converting rotary motion of the drive motor into linear motion. Therefore, the number of parts increases, the overall structure becomes complicated, the overall size and cost increase, and reliability is lowered.
An object of the present invention is to provide a drive motor which can simplify the overall structure of a drive apparatus utilizing the motor, can decrease the size and cost of the drive apparatus, and can improve the reliability of the drive apparatus.
Another object of the present invention is to provide a drive motor which can secure smooth rotational movement and smooth advancement/retraction movement, which has a short overall axial length, and which secures sufficient thrust in the advancement/retraction direction.
Still another object of the present invention is to prove a drive apparatus for a molding machine utilizing such a drive motor.
To achieve the above-described objects, the drive motor of the present invention has a shaft supported by a casing to be rotatable and movable in the axial direction over a predetermined stroke. A portion of the shaft is utilized in order to form a rotary motor section for rotating the shaft, and another portion of the shaft is utilized in order to form an electromagnetic plunger section for moving the shaft in the axial direction. The rotary motor section and the electromagnetic plunger section are integrally built in the casing.
A drive apparatus for a molding machine according to the present invention utilizes the above-described drive motor. The front end of the shaft is connected to the rear end of a screw disposed within a barrel of a plasticizing unit of a pre-plasticization-type injection molding machine. Through axial movement of the shaft, a resin passage of the barrel is opened and closed by a valve portion provided at the front end of the screw.
In another drive apparatus for a molding machine according to the present invention, the tip end of the shaft is connected to a mold exchange rotary table for supporting a plurality of molds.